Oxidation process

ABSTRACT

Methods of oxidizing alpha unsaturated aldehydes to the corresponding alpha unsaturated monocarboxylic acids are disclosed. The methods are characterized in one aspect by the use of a molybdenum phosphate catalyst. Methods of producing the alpha unsaturated aldehydes starting material from the corresponding unsaturated olefins are also disclosed.

United States Patent Parthasarathy et a1.

[ 51 May 30, 1972 [54] OXIDATION PROCESS [72] Inventors: R.Parthasarathy, Takoma Park; Frank G.

Ciapetta, Silver Spring, both of Md.

[52] US. Cl. ..260/530 N, 260/533 N, 260/604 R, 260/606 [51] Int. Cl.C07c 51/26, C07c 53/08 [58] Field ofSearch ..260/530 U,533 U, 604

[56] References Cited UNITED STATES PATENTS 3,395,178 7/1968 Callahan..260/530 U 2,881,212 4/1959 Idol et al.. ...260/530 U 3,293,290 12/1966Flint et a1 ..260/533 3,423,455 1/1969 Dobves et al. ..260/533 2,941,0076/1960 Callahan et al... ....260/604 3,427,343 2/1969 Callahan et al.......260/604 3,423,329 l/1969 Gruber ..260/ 604 FOREIGN PATENTS ORAPPLICATIONS 903,034 8/ 1962 Great Britain ..260/533 PrimaryExaminer-Lorraine A. Weinberger Assistant ExaminerR. S. WeissbergAtt0rney-Joseph P. Nigon and Kenneth E. Prince [57] ABSTRACT Methods ofoxidizing alpha unsaturated aldehydes to the corresponding alphaunsaturated monocarboxylic acids are disclosed. The methods arecharacterized in one aspect by the use of a molybdenum phosphatecatalyst. Methods of producing the alpha unsaturated aldehydes startingmaterial from the corresponding unsaturated olefins are also disclosed.

10 Claims, No Drawings OXIDATION PROCESS This invention relates to animproved process for the production of unsaturated oxygen containingcompounds comprising monocarboxylic acids. In one particular embodiment,the invention relates to an improved process for the direct vaporoxidation of acrolein and/or methacrolein to acrylic acid and/ormethacrylic acid respectively.

Unsaturated aliphatic monocarboxylic acids such as acrylic acid andmethacrylic acid, for example, are valuable starting and intermediatematerials for a whole series of reactions because of their highlyreactive nature. Their highly reactive nature also makes these materialsdifficult to prepare and contributes to the problems encountered inlarge scale production of these acids.

The prior art processes for the production of acrylic acid and/ormethacrylic acid have been based on operational procedures which arecomplex and costly and which do not lend themselves to economical largescale operation. These procedures generally comprise liquid phaseoperation which of necessity require relatively costly equipment and arevery difficult to control.

It has been recognized for sometime that a potential source ofunsaturated acids is the corresponding olefins. However, large scaleproduction of the acids directly from this group has not followedbecause of the relatively low yield and costly operational stepsinvolved in the available processes.

The prior art processes generally result in the generation of a mixedproduct that contains varying amounts of unsaturated aldehydes alongwith small amounts of unsaturated monocarboxylic acids. These processeswere frequently directed to separation and utilization of the aldehydesin the subsequent preparation of monocarboxylic acids. Procedures ofthis type were obviously cumbersome and commercially unattractive.

We have found that the selective oxidation of acrolein to acrylic acidand/or methacrolein to methacrylic acid can be effected and high yieldsof acrylic acid and methacrylic acid can be recovered by the vapor phasereaction in a single pass using molybdenum phosphate as the catalyst.

In this system, the aldehyde, in admixture with air and steam, is passedthrough the reactor containing the catalyst for conversion of thealdehyde to acid. Although our process is specific to the use ofmolybdenum phosphate catalyst for the preparation of the acid, it isalso useful as a catalyst for the second stage of a two stage system forthe oxidation of propylene to acrylic acid or of isobutylene tomethacrylic acid. For example, one suitable two-step process for theconversion of alpha olefinic hydrocarbons containing fewer than eightcarbon atoms in the molecule to a reactant mixture containingsubstantial amounts of alpha unsaturated monocarboxylic acidscorresponding to said olefinic hydrocarbons comprises reacting saidolefins in the vapor phase with oxygen in a two-stage sequential reactorsystem in the presence of a catalyst selected from the group consistingof bismuth molybdate, rare earth promoted bismuth molybdate or GroupVIII metal promoted bismuth molybdate in the first stage and a catalystconsisting essentially of a molybdenum phosphate having a molybdenumtrioxide to phosphorous pentoxide ratio of 1:1 to 1:5 in the secondstage.

The novelty for this invention resides in the use of molybdenumphosphate" catalyst for the conversion of acrolein to acrylic acid. Themolybdenum phosphate suitable for use in our process has an MoO to Pratio in the range of 1:1 to 1:5. The preferred ratio is in the range of1:1 to 1:3. We have also found that the acrylic acid selectivity isgreatly increased if the catalyst is calcined at a temperature of about1,200 F.

The catalyst component may be supported on any suitable support with anaverage pore size within 100 Angstroms such as, for example, alumina,silica gel, etc. The preferred support is silica gel having a porevolume of about 0.1 cc./g. to l cc./g. and surface area of about to 150Mlg. The compositions with varying ratios of M00 to P 0 are convenientlyprepared from ammonium molybdate and ammonium acid phosphate or by theuse of phosphomolybdic and phosphoric acids. Commercially availablemolybdenum phosphate is also a suitable starting material for thepreparation of these active catalysts.

One suitable method of preparing a catalyst having an M00, to P 0, ratioof 1:1 comprises mixing ammonium molybdate and ammonium acid phosphatewith a silica sol, gelling the resulting mixture and drying andcalcining the resulting product. The product having a M00 to P 0, ratioof l to 1.5 can be conveniently prepared by dissolving commerciallyavailable molybdenum phosphate in deionized water and addingphosphomolybdic acid. The mixture is then added to a silica sol and thepH adjusted. The gel is then dried and the product calcined to preparethe catalyst.

The final form of the catalyst is unimportant and may be manufactured inthe form of pellets or in the form of finely divided particles byconventional spray drying techniques. Extrusion or pellets may be usedto prepare our catalyst in the desired form. Furthermore, the novelty ofthis invention is not limited to molybdenum phosphate alone. Tungstenphosphates of varying ratios of M00 to P 0; are also envisaged. Thecatalyst may also be used in conjunction with catalytically inertsupports such as silicon carbide or like materials.

The oxygen for use in the process may be recovered from thefractionation of air but may be a more dilute oxygen containing gas. Asuitable source of oxygen comprises, for example, molecular oxygen aloneor as a mixture with an inert diluent gas such as nitrogen. Air may beused as the source of the molecular oxygen reactant. The oxygencontaining gas may be admixed with the aldehyde charge of the systembefore it is introduced into the reaction zone or it may be introducedin part or in its entirety directly into the reaction zone at one ormore points in the reaction zone. The oxygen containing gas is passedthrough the system in conjunction with steam. The ratio of oxygen tosteam in the gas conversion mixture is from 1:2 to 1:20, the preferredratio being 1:3 to 1:15. The amount of oxygen fed to the reactor basedon 1 mole of unsaturated aldehyde should be in the range of 0.25 molesto 5 moles. The best results are obtained when the mole ratio of oxygento unsaturated aldehyde is greater than 0.25 to 1 and less than about 2to l.

The process can be operated at any convenient pressure. Since noadvantage is derived from operation at pressures other than atmospheric,operation at atmospheric pressure is obviously preferred.

The process can be conducted at temperatures in the range of about 600to about l,000 F. The best results are obtained when the process iscarried out at temperatures of 600 to 900 F.

In this system, the aldehyde is present in an amount equal to about 2:20volume percent, preferably about 4:12 volume percent in a reactantmixture. The ratio of oxygen to aldehyde is maintained at a range of 0.5to 1 to 5 to 1. The preferred oxygen to aldehyde ratio is 1:1 to 2:1.The steam to aldehyde ratio is in the range of 2:1 to 20:1, preferably4:1 to 15:1. The reaction is carried out for a period of time such thatthe reactants contact the catalyst for periods of 1 to 10 seconds,preferably about 3 to 4 seconds. The contact time is defined as thereciprocal of the gas hourly space velocity at standard conditions.

As pointed out previously, the essence of the present invention is theconversion of acrolein and methacrolein from acrylic acid to methacrylicacid by the catalytic vapor phase oxidation in a single pass usingmolybdenum phosphate as a catalyst.

The invention is further illustrated by the following specific butnon-limiting examples.

EXAMPLE I This example describes one of the alternate methods ofpreparing the catalyst suitable for the conversion of acrolein.

A total of 61.5 grams of ammonium molybdate (NI-l Mo O -4H O) in cc. ofdeionized water was added to 210 grams of a commercially availablesilica sol purchased from the DuPont Company. This quantity of silicasol contains 100 grams of SiO A change (93 grams) of ammonium acidphosphate (NHJ HPOQ was dissolved in 125 m1. of deionized water, heatedto 70 C. and added to the above mixture. The pH of the resulting mixturewas 7.1. The pH was adjusted to 7.3 by the addition of 16 ml. of a 1:1ammonium hydroxide solution. A firm gel formed which was dried for 16hours at 220 F. and calcined for 16 hours at 1,000" F. and for 16 hoursat 1,200 P. The calcined product was cooled and the particles of the 6to 25 mesh range were separated. A total of 163.9 grams of catalyst wasrecovered from thisrun. The product contained 50 percent of a molybdenumphosphate (having a M to P 0 ratio of l: 1 and 50 percent SiO EXAMPLE 11This example describes a method of preparing the catalyst wherein theM00 to P 0 ratio was changed to a 3: 1.

A total of 69.5 grams of ammonia molybdate was dissolved in 100 m1. ofdeionized water and 158 grams (75 grams SiO of a commercially availablesilica sol purchased from the Du- Pont Company was added. A total of34.4 grams of ammonium acid phosphate was dissolved in 50 cc. ofdeionized water, heated to 70 C. and added to the silica ammoniummolybdate mixture. Gelation occurred without the addition of ammoniumhydroxide. The product was dried for 16 hours at 220 F. and calcined for16 hours at 1,000 F. The particles in the 6 to 25 mesh range wereseparated and used as the catalyst. A total of 140.6 grams of theproduct was recovered. The M00 to P 0 ratio of the catalyst was 3:1. Theproduct contained 50 percent active components and 50 percent SiOEXAMPLE III This example illustrates another method of preparing themolybdenum phosphate catalyst of our invention. A total of 36.3 grams ofcommercially available molybdenum phosphate was dissolved in a 100 ml.of deionized water and 25.6 grams of phosphomolybdic acid was added.This mixture was added to 222 grams 105 grams SiO of a silica sol soldby the Du- Pont Company. The pH of the mixture was 0.35. The mixture washeated to 150 F. and the pH adjusted to 6.2 by the addition of a 1:1solution of ammonium hydroxide. A gel formed which was dried for 16hours at 220 F. and calcined for 16 hours at 1,000 F. The particles inthe 6 to 25 mesh size range were separatedand used as the catalyst. Atotal of 141 grams of the product was recovered from this separation.The M00 to P 0 ratio in this preparation was 1 to 1.5. The catalystcontained 30 percent active ingredients and 70 percent silica.

EXAMPLE IV The efficiency of this catalyst was demonstrated by charging50 ml. of each of the catalyst preparations to an aluminized stainlesssteel reactor, and continuously contacting the catalyst with a feedmixture containing 5 percent acrolein, 25 percent air and 70 percentsteam at atmospheric pressure. The contact time was 3.6 seconds, thetemperature was varied in this series of runs. The results of thisseries of runs is set out in the table below:

yield. Here, propylene admixed with air and steam in amounts to give afeed mixture containing 5 percent propylene, 50 percent air and 45percent steam, was passed over a samarium promoted bismuth molybdatecatalyst (which is described in our copending case) maintained at 905 F.in the first stage of the two-stage system. The acrolein rich effluentwas then rapidly quenched to 250 F. and directly passed, withoutintermediate product separation, into the second reactor containing amolybdenum phosphate catalyst (having a M00 to P 0; ratio of 1 to 1.5)maintained at 775 F. An overall propylene conversion of 92 percent wasobtained giving 48 percent yield of acrylic acid based on convertedpropylene.

Obviously many modifications and variations of the invention may be madewithout departing from the essence and scope thereof.

What is claimed is:

1. A process for the conversion of alpha unsaturated aldehydescontaining fewer than eight carbon atoms in the molecule to a reactantmixture containing substantial amounts of alpha unsaturatedmonocarboxylic acids corresponding to said aldehydes which comprisesreacting said aldehydes in the vapor phase with an oxygen containing gasat a temperature of 700 to 900 F. in a bed of a catalyst consistingessentially of a molybdenum phosphate catalyst having a molybdenumtrioxide to phosphorus pentoxide ratio of 1:1 to 1:5.

2. The process of claim 1 wherein the reaction is carried out as asecond stage of a two-stage process having a first stage and said secondstage.

3. The process according to claim 1 wherein the oxygen containing gas isair.

4. The process according to claim 2 wherein the oxygen containing gas isadmixed with steam in a ratio of 1:2 to 1:20 and a catalyst consistingessentially of a molybdenum phosphate having a molybdenum trioxide tophosphorus pentoxide ratio of 1:1 to 1:5 in the second stage.

5. The process according to claim 1 wherein the aldehyde is selectedfrom the group consisting of acrolein and methacrolein.

6. The process according to claim 1 wherein the catalyst contains 10 to90 percent active ingredients and a S102 diluent.

7. A process for the conversion of alpha olefinic hydrocarbonscontaining fewer than eight carbon atoms in the molecule to a reactantmixture containing substantial amounts of alpha unsaturatedmonocarboxylic acids corresponding to said olefinic hydrocarbons whichcomprises reacting said olefins in the vapor phase with oxygen in atwo-stage sequential reactor system in the presence of a catalystconsisting essentially of rare earth promoted bismuth molybdate in thefirst stage and a catalyst consisting essentially of a molybdenumphosphate having a molybdenum trioxide to phosphorus pentoxide ratio of1:1 to 1:5 in the second stage.

8. The process according to claim 2. wherein the feed to said firststage is selected from the group consisting of propylene and isobutyleneand the oxygen containing gas is air.

TABLE I Selectivity ol Acroleln conversion MOOz/ Ave. bed Percent P205temp. acrolein Acrylic Acetic O thcr Catalyst ratio F converted acidacid CHzC HO products 50% MOOazPzOs 0n sic..- 1:1 814 S3 75. 5 l3. 8 l.0 9. 2 30% 2MoOa:3P2O on $10? 1:1. 5 784 71. 5 75. 3 J. 0 2. u 12. 4 20%lVIOO313P205 0n SiO-z. 3:1 861 75 77. 7 l5. 7 2. 2 4. 2

C0 CO2 and formaldehyde. 7

It is obvious from review of the data that conversion of greater thanpercent can be effected using the catalyst of this invention.

EXAMPLE V This example illustrates the efficiency of the molybdenumphosphate catalyst in the second stage of a two-stage system for thedirect oxidation of propylene to acrylic acid in high

2. The process of claim 1 wherein the reaction is carried out as asecond stage of a two-stage process having a first stage and said secondstage.
 3. The process according to claim 1 wherein the oxygen containinggas is air.
 4. The process according to claim 2 wherein the oxygencontaining gas is admixed with steam in a ratio of 1:2 to 1:20 and acatalyst consisting essentially of a molybdenum phosphate having amolybdenum trioxide to phosphorus pentoxide ratio of 1:1 to 1:5 in thesecond stage.
 5. The process according to claim 1 wherein the aldehydeis selected from the group consisting of acrolein and methacrolein. 6.The process according to claim 1 wherein the catalyst contains 10 to 90''percent active ingredients and a SiO2 diluent.
 7. A process for theconversion of alpha olefinic hydrocarbons containing fewer than eightcarbon atoms in the molecule to a reactant mixture containingsubstantial amounts of alpha unsaturated monocarboxylic acidscorresponding to said olefinic hydrocarbons which comprises reactingsaid olefins in the vapor phase with oxygen in a two-stage sequentialreactor system in the presence of a catalyst consisting essentially ofrare earth promoted bismuth molybdate in the first stage and a catalystconsisting essentially of a molybdenum phosphate having a molybdenumtrioxide to phosphorus pentoxide ratio of 1:1 to 1:5 in the secondstage.
 8. The process according to claim 2 wherein the feed to saidfirst stage is selected from the group consisting of propylene andisobutylene and the oxygen containing gas is air.
 9. The processaccording to claim 2 wherein the first stage of the reactor is operatedat a temperature of 700* to 950* F. and the second stage at atemperature of 700* to 900* F. and the feed is the olefin, air andsteam.
 10. The process according to claim 2 wherein the feed to saidfirst stage is a mixture of propylene, air and steam and the ratio ofoxygen to propylene is in the range of 0.5:1 to 5:1.